As one of the trench-gate type IGBTs, a so-called thinning structure has been given as described below, in which with respect to a structure where a plurality of cell regions that act as IGBT elements are continuously disposed, certain cell regions are periodically thinned out from the plurality of continuous cell regions. This structure is disclosed in, for example, U.S. Pat. No., 6,737,705 and Japanese Patent Application Publication No. 2003-204066. Specifically, in the thinning structure, some cell regions are removed periodically from continuously arranged multiple cells.
The above IGBT has a P+-type substrate, an N−-type drift layer disposed on a surface of the P+-type substrate, a P-type base region disposed on a surface of the N−-type drift layer, N+-type emitter regions situated at an inner surface side of the P-type base region, trenches in a depth from a surface of the P-type base region to the N−-type drift layer through the N+-type emitter regions and the P-type base region, gate insulating films formed on inner walls of the trenches, gate electrodes formed within the trench and on the gate insulating film, an emitter electrode disposed on the surface of the P-type base region and electrically connected to a part of the P-type base region and the N+-type emitter regions, and a collector electrode disposed immediately on a back of the P+-type substrate and electrically connected to the P+-type substrate.
In the IGBT, the P-type base region is electrically divided into two types of regions (i.e., a first and a second regions) by the trenches, and the N+-type emitter regions and a P-type body region are formed in only one region (i.e., first region) between the two types of regions. The first region is electrically connected to the emitter electrode via the P-type body region. The N+-type emitter regions are disposed partially in a region near the trenches in the first region and channels are formed in portions where the region is contacted to the trenches. The first region in which an IGBT element is formed in this way corresponds to the cell region.
In the layout of the IGBT, a plurality of first regions and second regions of the P-type base regions are alternately disposed in a stripe pattern, and each of the second regions is enclosed by the trench.
In this way, as one of structures of the IGBT, a structure may be considered, in which each of the second regions is enclosed by the trench, thereby each of the second regions is configured by an independent P-type well and electrically isolated from the first regions or the second regions.
However, when the IGBT is formed in the above layout structure, the following two difficulties may be considered to arise.
That is, since each of the second regions is separated, electrical potential of each of the second regions is sometimes varied, for example, during switching operation of the IGBT. Therefore, a difficulty that operation of each cell within an IC chip becomes uneven may arise.
When a floating condition of each of the second regions is tested, since a plurality of second regions are tested at the same time, a method may be considered, in which each of the second regions is provided with a contact, and the second regions are electrically connected to each together by metal wiring such as Al wiring. Thus, for example, one test pad that has been electrically connected to the second regions is electrically connected to a tester, thereby a test can be easily performed.
However, when a special wiring line for electrically connecting the second regions to each together is provided within the IC chip, since restriction is caused in a layout of other wiring lines, a difficulty of decrease in degree of freedom may arise in a wiring layout.
Even when each of the second regions of the P-type base regions is configured by a separated P-type well enclosing each of the second regions by the trench, and separating the P-type wells forming respective second regions from one another, the difficulties may arise again.